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The seized Sailing Yacht A is among the creme de la creme of private yachts - seen here off Denmark

Gibraltar has impounded a Russian billionaire's superyacht - one of the world's biggest - because the German shipbuilder says he still owes 15.3m euros (£13.3m; $16.3m) in fees.

The claim has kept Andrey Melnichenko's Sailing Yacht A stuck in Gibraltar, a British territory, since Wednesday.

His spokesman voiced confidence that the order would be lifted soon.

The Bermuda-registered vessel, built by Nobiskrug, left the Kiel shipyard in northern Germany two weeks ago.

It is 143m (469ft) long and has three masts, the main one 100m high.

The superyacht, boasting a gross tonnage of 12,600, is reported to have cost at least €400m. Nobiskrug says it has an underwater observation pod, hybrid diesel-electric propulsion and "state-of-the-art" navigation systems. It was designed by Philippe Starck.

According to documents seen by Germany's NDR news, Nobiskrug is demanding an outstanding payment of €9.8m, as well as €5.5m for subcontractors and interest charges. Valla Yachts Ltd, a Bermuda company, is the yacht's registered owner.

A top Gibraltar court official, Admiralty Marshal Liam Yeats, told the BBC on Monday: "The vessel is under arrest and is currently at anchor in British Gibraltar Territorial Waters."

A spokesman for Mr Melnichenko described it as "a technical problem".

He told the BBC: "We are confident that the yacht will be handed over to the owner's project team in the coming days and this unfortunate episode will be over."

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The wealthy Russian also owns Motor Yacht A - seen here next to HMS Belfast on the Thames

Image copyrightAFPImage caption
Motor Yacht A was an imposing sight on the Thames last September

Mr Melnichenko, an industrialist with big stakes in Russia's fertiliser, coal and energy sectors, has a $13.2bn fortune, business website Forbes reports.

Mr Melnichenko also owns a 5,500-tonne superyacht called Motor Yacht A, which is reportedly up for sale. It was built by Germany's Blohm & Voss shipyard and launched in 2008.

It is 119m long - smaller than Sailing Yacht A - and was also designed by Philippe Starck. In September 2016 it moored alongside the old British light cruiser HMS Belfast on the River Thames, in central London.

What happens when a ship is arrested?

The Gibraltar Port Authority says ship arrests happen when "banks and creditors seek recompense from shipowners who find themselves unable to pay up on mortgages or loans".

"Most arrested ships are sold in a sealed-bids auction within six to eight weeks, once the claim has been proved and judgment given."

In a statement on its website, it says "we put 'ship keepers' on board - two security guards to protect the vessel and its contents.

"We provide the crew with everything, from bunkers (fuel storage compartments) so they can keep the generators going, to provisions of food and water."

A launch is also arranged "so that the crew, who would otherwise be stuck onboard, can have some shore leave".